Local hydrophobicity allows high-performance electrochemical carbon monoxide reduction to C2+ products.

While CO can already be produced at industrially relevant current densities via CO2 electrolysis, the selective formation of C2+ products seems challenging. CO electrolysis, in principle, can overcome this barrier, hence forming valuable chemicals from CO2 in two steps. Here we demonstrate that a mass-produced, commercially available polymeric pore sealer can be used as a catalyst binder, ensuring high rate and selective CO reduction. We achieved above 70% faradaic efficiency for C2+ products formation at j = 500 mA cm-2 current density. As no specific interaction between the polymer and the CO reactant was found, we attribute the stable and selective operation of the electrolyzer cell to the controlled wetting of the catalyst layer due to the homogeneous polymer coating on the catalyst particles' surface. These results indicate that sophistically designed surface modifiers are not necessarily required for CO electrolysis, but a simpler alternative can in some cases lead to the same reaction rate, selectivity and energy efficiency; hence the capital costs can be significantly decreased.

Fundamentals and utilization of solid/ liquid phase boundary interactions on functional surfaces.

The affinity of macroscopic solid surfaces or dispersed nano- and bioparticles towards liquids plays a key role in many areas from fluid transport to interactions of the cells with phase boundaries. Forces between solid interfaces in water become especially important when the surface texture or particles are in the colloidal size range. Although, solid-liquid interactions are still prioritized subjects of materials science and therefore are extensively studied, the related literature still lacks in conclusive approaches, which involve as much information on fundamental aspects as on recent experimental findings related to influencing the wetting and other wetting-related properties and applications of different surfaces. The aim of this review is to fill this gap by shedding light on the mechanism-of-action and design principles of different, state-of-the-art functional macroscopic surfaces, ranging from self-cleaning, photoreactive or antimicrobial coatings to emulsion separation membranes, as these surfaces are gaining distinguished attention during the ongoing global environmental and epidemic crises. As there are increasing numbers of examples for stimulus-responsive surfaces and their interactions with liquids in the literature, as well, this overview also covers different external stimulus-responsive systems, regarding their mechanistic principles and application possibilities.

Development of a Hydrophobicity-Controlled Delivery System Containing Levodopa Methyl Ester Hydrochloride Loaded into a Mesoporous Silica.

BACKGROUND: The drug release of antiparkinsonian drugs is an important issue during the formulation process because proper release kinetics can help to reduce the off periods of Parkinson's disease. A 2-factor, 3-level (32) full-factorial design was conducted to evaluate statistically the influence of the hydrophobicity of mesoporous silica on drug release. METHODS: Hydrophobization was evaluated by different methods, such as contact angle measurement, infrared spectroscopy and charge titration. After loading the drug (levodopa methyl ester hydrochloride, melevodopa hydrochloride, LDME) into the mesopores, drug content, particle size, specific surface area and homogeneity of the products were also analyzed. The amorphous state of LDME was verified by X-ray diffractometry and differential scanning calorimetry. RESULTS: Drug release was characterized by a model-independent method using the so-called initial release rate parameter, as detailed in the article. The adaptability of this method was verified; the model fitted closely to the actual release results according to the similarity factor, independently of the release kinetics. CONCLUSIONS: The API was successfully loaded into the silica, resulting in a reduced surface area. The release studies indicated that the release rate significantly decreased (p < 0.05) with increasing hydrophobicity. The products with controlled release can reduce the off period frequency.

A Stimulus-Responsive Polymer Composite Surface with Magnetic Field-Governed Wetting and Photocatalytic Properties.

With the increasing demand for liquid manipulation and microfluidic techniques, surfaces with real-time tunable wetting properties are becoming the focus of materials science researches. In this study, we present a simple preparation method for a 0.5-4 µm carbonyl iron (carbonyl Fe) loaded polydimethylsiloxane (PDMS)-based magnetic composite coating with magnetic field-tailored wetting properties. Moreover, the embedded 6.3-16.7 wt.% Ag-TiO2 plasmonic photocatalyst (d~50 nm) content provides additional visible light photoreactivity to the external stimuli-responsive composite grass surfaces, while the efficiency of this photocatalytic behavior also turned out to be dependent on the external magnetic field. The inclusion of the photocatalyst introduced hierarchical surface roughness to the micro-grass, resulting in the broadening of the achievable contact and sliding angle ranges. The photocatalyst-infused coatings are also capable of catching and releasing water droplets, which alongside their multifunctional (photocatalytic activity and tunable wetting characteristics) nature makes surfaces of this kind the novel sophisticated tools of liquid manipulation.

Photocatalytic elimination of interfacial water pollutants by floatable photoreactive composite nanoparticles.

Disastrous oil spills cause severe environmental issues. The shortcomings of current cleaning methods for remediating oil have prompted the latest research drive to create intelligent nanoparticles that absorb oil. We, therefore, synthesized 197 ± 50 nm floatable photoreactive hybrid nanoparticles with Ag-TiO2 plasmonic photocatalyst (Eg = 3.08 eV) content to eliminate interfacial water pollutants, especially toluene-based artificial oil spill. We found that the composite particles have non-wetting properties in the aqueous media and float easily on the surface of the water due to the moderate hydrophobic nature (Θ = 113°) of the matrix of polystyrene, and these properties lead to elevated absorption of the interfacial organic pollutants (e.g., mineral oil). We showed that (28.5 mol%) divinylbenzene cross-linker content was required for adequate swelling capacity (2.15 g/g), whereas incorporated 15.8% Ag-TiO2 content in the swollen particles was enough for efficient photodegradation of the artificial oil spill under 150 min LED light (λmax = 405 nm) irradiation. The swollen polymer particles with embedded 32 ± 7 nm Ag-TiO2 content increase the efficiency of photooxidation by increased the direct contact between both the photocatalysts and the artificial oil spill. Finally, it was also presented that the composite particles destroy themselves: after approximately one and a half months of continuous LED light irradiation, the organic polymer component of the composite was almost completely (88.5%) photodegraded by the incorporated inorganic photocatalyst particles.

Fast optical method for characterizing plasmonic nanoparticle adhesion on functionalized surfaces.

In this paper, a rapid optical method for characterizing plasmonic (gold) nanoparticle (AuNP) adhesion is presented. Two different methods were used for AuNP preparation: the well-known Turkevich method resulted in particles with negative surface charge; for preparing AuNPs with positive surface charge, stainless steel was used as reducing agent. The solid surface for adhesion was provided by a column packed with pristine or surface-modified glass beads. The size of the nanoparticles was studied by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS); the surface charge of the components was determined by streaming potential measurements. The characterization of adhesion was performed in a flow system by UV-Vis spectroscopy. During the adhesion experiments, the role of the surface charge, the particle size, and the pH were studied, as well as the adhered amount of gold nanoparticles and the surface coverage values. The latter was estimated by theoretical calculations and defined by the quotient of the measured and the maximal adhered amount of nanoparticles, which could be determined by the cross-sectional area of the NPs and the specific surface area of the glass beads. The results are verified by the polarization reflectometric interference spectroscopy (PRIfS) method: silica nanoparticles with diameters of a few hundred (d~450) nanometers were immobilized on the surface of glass substrate by the Langmuir-Blodgett method, the surface was modified similar to the 3D (continuous flow packed column) system, and gold nanoparticles from different pH solutions were adhered during the measurements. These kinds of modified surfaces allow the investigation of biomolecule adsorption in the same reflectometric setup. Graphical abstract.

Microwave-assisted synthesis of biologically relevant steroidal 17-exo-pyrazol-5'-ones from a norpregnene precursor by a side-chain elongation/heterocyclization sequence.

Multistep syntheses of novel 17ß-pyrazol-5'-ones in the Δ5-androstane series were efficiently carried out from pregnenolone acetate. A steroidal 17-carboxylic acid was first synthesized as a norpregnene precursor by the bromoform reaction and subsequent acetylation. Its CDI-activated acylimidazole derivative was then converted to a ß-ketoester containing a two carbon atom-elongated side chain than that of the starting material. A Knorr cyclization of the bifunctional 1,3-dicarbonyl compound with hydrazine and its monosubstituted derivatives in AcOH under microwave heating conditions led to the regioselective formation of 17-exo-heterocycles in good to excellent yields. The suppression of an acid-catalyzed thermal decarboxylation of the ß-ketoester and thus a significant improvement in the yield of the desired heterocyclic products could be achieved by the preliminary liberation of the arylhydrazines from their hydrochloride salts in EtOH in the presence of NaOAc. The reaction rates were found to depend on the electronic character of the substituent present in the phenylhydrazine applied. The antiproliferative activities of the structurally related steroidal pyrazol-5'-ones and their deacetylated analogs were screened on three human adherent breast cancer cell lines (MCF7, T47D and MDA-MB-231): the microculture tetrazolium assay revealed that some of the presented derivatives exerted cell growth inhibitory effects on some of these cell lines comparable to those of the reference compound, cisplatin.

Preparation of novel tissue acidosis-responsive chitosan drug nanoparticles: Characterization and in vitro release properties of Ca2+ channel blocker nimodipine drug molecules.

The pH-responsive intelligent drug release facility of hydrophobically modified chitosan nanoparticles (Chit NPs) (d = 5.2 ±â€¯1.1 nm) was presented in the case of poorly water soluble Ca2+ channel blocker nimodipine (NIMO) drug molecules. The adequate pH-sensitivity, i.e. the suitable drug carrier properties of the initial hydrophilic Chit were achieved by reductive amination of Chit with hexanal (C6-) and dodecanal (C12-) aldehydes. The successful modifications of the macromolecule were evidenced via FTIR measurements: the band appearing at 1412 cm-1 (CN stretching in aliphatic amines) in the cases of the hydrophobically modified Chit samples shows that the CN bond successfully formed between the Chit and the aldehydes. Hydrophobization of the polymer unambiguously led to lower water contents with lower intermolecular interactions in the prepared hydrogel matrix: the initial hydrophilic Chit has the highest water content (78.6 wt%) and the increasing hydrophobicity of the polymer resulted in decreasing water content (C6-chit.: 74.2 wt% and C12-chit.: 47.1 wt%). Furthermore, it was established that the length of the side chain of the aldehyde influences the pH-dependent solubility properties of the Chit. Transparent homogenous polymer solution was obtained at lower pH, while at higher pH the formation of polymer (nano)particles was determined and the corresponding cut-off pH values showed decreasing tendency with increasing hydrophobic feature (pH = 7.47, 6.73 and 2.49 for initial Chit, C6-chit and C12-chit, respectively). Next the poorly water soluble NIMO drug was encapsulated with the C6-chit with adequate pH-sensitive properties. The polymer-stabilized NIMO particles with 10 wt% NIMO content resulted in stable dispersion in aqueous phase, the formation of polymer shell increased in the water solubility/dispersibility of the initial hydrophobic drug. According to the drug release experiments, we clearly confirmed that the encapsulated low crystallinity NIMO drug remained closed in the polymer NPs at normal tissue pH (pH = 7.4, PBS buffer, physiological condition) but at pH < 6.5 which is typical for seriously ischemic brain tissue, 93.6% of the available 0.14 mg/ml NIMO was released into the buffer solution under 8 h release time. According to this in vitro study, the presented pH-sensitive drug carrier system could be useful to selectively target ischemic brain regions characterized by acidosis, to achieve neuroprotection at tissue zones at risk of injury, without any undesirable side effects caused by systemic drug administration.